Floating cover structures



1954 A. M. SOUTHWORTH EIAL 3,120,902

FLOATING COVER STRUCTURES 4 Sheets-Sheet 1 Filed Jan. 9, 1961 INVENTORS ALFRED M. SOUTHWOR'TH CHARLES E. SABIN W Z n7 ATTO EY' Feb. 11, 1964 A. M. SOUTHWORTH m-AL FLOATING COVER STRUCTURES 4 Sheets-Sheet 2 Filed Jan. 9, 1961 INVENTORS ALFRED M.SOUTHWORTH CHARLES E. SABIN ATTO NEY 11, 1964 A. M. SOUTHWORTH EIAL 3,120,902

FLOATING COVER STRUCTURES Filed Jan. 9, 1961 4 Sheets-Sheet 3 INVENTORS ALFRED M. SOUTHWORTH CHARLES E. SABIN 1964 A. M. SOUTHWORTH ETAL 3, ,902

FLOATING COVER STRUCTURES 4 Sheets-Sheet 4 Filed Jan. 9, 1961 INVENTORS ALFRED M. SOUTHWORTH CHARLES E. SABIN ATTORNEY United States Patent 3,120,902 FLOATING CQVER STlEUtITURES Alfred M. Southworth, 293 S. Dale Mshry, Tampa, Fla,

and Charles E. Sabin, Tampa, Fla; said Sabin assignor to said douthworth Filed Jan. 9, 19st, Ser. No. 81,647 Claims. (6i. ZZtl-Zti) This invention relates to improved floating covers for use in tanks such as sewage digesters and the like, and more particularly to novel constructions and arrangements of parts in such covers by reason of which more versatile, economical, and useful covers are achieved.

Heretofore, the construction of covers adapted to float on the surface of matter contained in digester tanks has been an expensive and time-consuming procedure, usually entailing laborious construction practices utilizing conventional rigid building materials such as steel, wood and the like, with the size of the cover requiring the building process to be conducted at the site and often within the tank itself. Moreover, the conventional cover resulting from such construction has presented inordinate problems of removal for permitting the necessary periodic cleaning of the tank, which is usually accomplished through the open top thereof with a clam shell type digger or the like. Accordingly, the present invention aims to provide an improved floating cover structure for sewage digestion tanks and the like, which cover is readily assembled and disassembled and is otherwise relatively inexpensive by reason of the simplicity of the components thereof which include an inflatable cell or cells formed of normally limp sheet material, such as vinyl plastic or the like, which is compatible with the matter to be contained in the tank, the cell or cells being distended into a semi-rigid condition by gas under pressure and being surrounded by a peripheral rigid ring member which is in guided relationship with the walls of the tank for governing vertical movements of the cover with changes in the level of mat ter contained in the tank.

Another object of this invention is the provision of a cover of the above-mentioned character comprising a plurality of discrete wedge-shaped cells disposed in a circular array about a rigid central member which acts as a hub and to which the cells may be connected for delivery to and lowering into a tank prior to inflation, the cells thereafter being inflated and brought into engagement with the rigid outer ring member.

As another object, this invention aims to provide a floating cover structure including inflatable and collapsible cell portions which may be distended by gas under pressure to assume semi-rigid shapes and which can be individually ballasted by pumping liquid such as water into and out of the individual cells, whereby one or more of the cells may be collapsed and furled to provide access to the interior of the tank for cleaning, repairs and the like, which the remaining cells can be ballasted to provide for trimming or leveling of the cover during such procedures.

Still another object of the invention is the provision of improved floating covers for digestion tanks having infiatable components and rigid components, the former including one or more air cells and the latter including an outer ring having guide means thereon for cooperation with the tank wall and having means for controlling the presence of scum between the ring and the wall, the rigid components including also means for maintaining a predetermined pressure within the air cells and means for collecting gases generated within the tank.

Other objects and advantages of the novel constructions and arrangements of parts of this invention will be app cut for the following description of the presently preferred embodiments thereof and from the accompanying sheets of drawings forming a part of this specification, and in which FIG. 1 is an elevational view of a digestion tank having a floating cover structure embodying the present invention, with portions broken away to better illustrate the construction thereof;

FIG. 2 is atop plan view of a tank and cover illustrated in FIG. 1;

FIG. 3 is a sectional view of a portion of the tank and cover on an enlarged scale and taken substantially along line 3-3 of FIG. 2;

FIG. 4 is a sectional view showing details of construction of a portion of the cover taken along line 4-4 of FIG. 2 and on a still larger scale;

FIG. 5 is an enlarged sectional view of a manhole portion of the cover taken along line 5-5 of FIG. 2;

FIG. 6 is a plan view of a different embodiment of the invention;

FIG. 7 is a sectional view of the embodiment of FIG. 6 and taken along line 7-7 thereof;

FIG. 8 is a sectional view of still another embodiment of the invention;

FIG. 9 is a sectional view on an enlarged scale of a portion of the embodiment of cover illustrated in FIG. 8;

FIG. 10 is a sectional view of still another embodiment of the invention;

FIG. 11 is an enlarged sectional view of a portion of the tank and cover of FIG. 2 taken along line l111 thereof; and

FIG. 12 is a sectional view taken along line 12l2 of FIG. 11.

Floating covers embodying the present invention are adapted for use with tanks used for storage or other purposes but are particularly useful in conjunction with tanks known as digesters and used in the process of digesting sewage and the like. In the form of the invention illustrated in FIGS. 1 through 5, there is illustrated a digestion tank having vertical wall portions 11, which in this instance are cylindrical but may be of other configurations. A floating cover embodying the present invention is indicated generally at 1.2 and comprises a circular array of in flated cells 13 surrounding a rigid centrally located member or hub 14:, and encompassed by a rigid outer or peripheral ring 15. Cells 13 are generally wedge-shaped in plan and are formed of normally limp, gas impervious plastic sheet material, such as vinyl, nylon, and the like, which is compatible with the liquids or matter contained in tank 11. The cells are connected to hub 14 and ring 15 and are inflated by air or other gas under pressure so as to be distended and form a relatively rigid cover structure and so as to provide flotation or buoyancy for the cover which is adapted to float on the surface of the liquid contained in the tank.

As is best shown in FIG. 3, each cell comprises an upper wall 13a which slopes downwardly and outwardly from the upper edge of a vertical arcuate inner end wall 13b, and a lower wall 13c, which extends outwardly from the lower edge of inner end wall 3%. Wall preferably slopes downwardly from wall 1311 but to a substantially lesser degree than does wall 33a. Wale 13a and 13c are connected at their outer edges by a wall 13d, and along their radially extending edges by vertical walls 132, so that each cell 13 is a complete, discrete unit capable of being independently inflated or collapsed. The cells may each be molded as a whole, or the walls may be separately formed and cemented or welded together to form each cell.

The central member of hub 14, to which the inner ends of the cells 13 are connected, is hollow and is preferably formed of sheet metal or glass fiber reinforced plastic. Hub 1d conveniently comprises an upper stepped section and a lower cylindrical section 1%. The

stepped upper section 14a includes a cylindrical dome portion 14c defining a gas collection chamber 16, and a skirt portion 14d which is of larger diameter than the dome portion and includes an outwardly directed flange FAQ about the lower edge thereof. The lower cylindrical section 1415 of hub 14-, which is open to the interior of tank ill for admitting gases generated by the digesting processes therein and which rise to the collection chamber 16, is secured to flange Me of skirt 14d by a mating flange 14;. Section 141: has a flange Mg about its lower edge which, together with flange 14f, defines annular, outwardly facing groove in which the inner ends of cells 13 are received. The inner ends of cells 13 are fixed to the hub member 14 between flanges M1 and 14g thereof by many suitable means, but preferably have the end walls 13:; thereof secured to the hub section 14b by means of a cement or adhesive. A pressure relief valve and flame arresting assembly 17 is conveniently mounted atop dome 14c and is provided with a flexible conduit 17a for carrying off collected gas for burning or other disposition.

The cells 13 are adapted to be inflated into their distended condition and to have the proper pr ssure maintained therein by a motor driven air compressor 19 which is mounted, in this instance, on the shoulder between dome 14c and skirt portion 14:! of hub 14. A pressure line or conduit 19:! leads from compressor 19 to a tubular ring or header 26 which is mounted inside cylindrical section 14/), and is in communication through ports Zila with each of the individual cells 13. Ports 200 are preferably under the control of remotely operated valves Zilb so that cells may be independently inflated or deflated. Normally, compressor w is under the control of a pressurestat, not shown, of any conventional construction, which senses the pressure in the cells and controls the operation of the compressor which supplies air through header 2%) to maintm'n the pressure in the cells above a predetermined value. valve 1% is located in line 1% and is adapted to bleed of}? pressures in the cells exceeding another predetermined value. By this arrangement the cover 12 of the digester It) may be operated as a self-contained or independent unit, although it will be understood that an outside source of air pressure may be utilized in the practice of this invention.

The outer ring 15, to which the outer ends of the inflated cells 13 are attached, is preferably formed of metal and comprises upper and lower inwardly directed flanges a, 15b connected by a web 15c so as to define an inwardly facing annular groove in which the outer ends of the cells are received. Although they may be otherwise secured, the cells are connected to the ring 15 as is best illustrated in FIG. 4. Flaps 22 are affixed, as by a suitable bonding adhesive, to walls 13a of the cells adjacent flange 15a, and are provided with eyelets or grommets 22a overlying that flange. Studs 23 extend upwardly from flange 15a and through the grommets 22a, A nut and washer on each stud 23 secures the flap 22 to the flange 15a and the cells 13 are thereby retained in engagement with the ring 15.

The ring 15 is disposed in a horizontal plane within tank It) and includes roller means 25 at the upper edge thereof in engagement with the tank wall 11 to reduce friction between the wall and cover 12, the cover being guided by the wall for vertical movement with increases and decreases in the surface level of liquid within the tank. Of course, any suitable number of such roller means may be disposed about the circumference of the cover structure. Additional guide roller means 26, best shown in FIGS. 11 and 12, are provided on ring 15 and are adapted to engage a removable vertical rib 27 which is secured to the inner surface of wall 11 and cooperates with the roller means as to prevent rotation of cover 12.. It will be understood that other conventional forms of anti-rotation means may be employed for this A pressure relief.

purpose. A plurality of skid members 2d are fixed to the lower edge of ring 15 and serve to aid in guiding the cover 12 with respect to the side walls of the tank.

A depending annular scum retaining balile 29 is secured, as by welding, to the lower edge of ring 15 and lies in close proximity to the wall 11 and acts to reduce the amount of scum and foam rising between the ring and the wall.

The buoyancy and level of floating covers 12 embodying this invention can be conveniently adjusted and trimmed to insure proper registry with the tank wall 11 during cleaning operations as will become apparent as the descript on proceeds. To these ends, an annular pipe or header 31 is secured to the lower portion of ring 1d, outside the scum retaining battle 2-9, and is in communication with the interior of each of the individual cells 13 through tubes Ella. An upright pipe or conduit 32 leads from header 33 between ring 15 and wall 11, and is connected to a flexible conduit 32a for conveying ballast liquids, such as water, to and from the interior of the cells for varying the buoyancy of the cover 12. The tubes 31a are preferably under the control of individual, remotely operated, valves 31!) so that ballast can be apportioned to the various cells as desired to level or trim the cover 12.

The above described ballasting or trimming, together with the flexible nature of the component cells 13, permits easy access to the interior of ti e digester tank without expensive and time-consuming disassembly. Thus, one or more of the cells 13 may be deflated or collapsed and furled back to provide access to the tank by a clam shell digger, dredge tube or the like, with the cover 12. being maintained level by trimming down cells opposite to the furlecl cells with ballast. At such a time the antirotation guide rib 27 may be removed to permit rotation of the cover 12 so that all portions of the tank may be conveniently reached through the opening provided by the furled cells.

in addition, one or more of the cells 13 may be provided with a manhole or access trunk 34. Trunk 34 comprises a circular, tapered wall member 34a having an annular flange 34b at the top thereof and disposed in a tapered tunnel 35 formed in the cell 13. Flange 34b overlies the top wall 13a of the cell and supports a cover plate 36 which may be dogged thereagainst in any suitable manner.

flhe various components of the cover, including the ring member 15, the individual cells 13, and the central memher or hub 14, are relatively light in weight, and, with the exception of ring 15, can be completely fabricated at the place of manufacture. Only the assembly of ring 15 from pre-forined sections need be carried out on the ground alongside the tank in which the cover is to be installed, or in the case of extremely large tanks, may be assembled in the tank itself. In carrying out the installation, the ring member 15 may be assembled and lowered into the tank where it is permitted to rest with bafile 29 thereof on corbels 37 extending inwardly from the Walls ill. The central member 14 with the deflated and furled cells 13 already attached thereto may then be hoisted over the tank by a crane and lowered into its proper position with respect to ring 15. The cells 13 may then be engaged and secured in the groove in member 15 and inflated with compressed air or the like, distending them and causing them to assume their previously described 7 shapes. Water, or the liquid matter which is to be contained in the tank, is then directed into the tank and the surface level thereof is raised until the cover 12 is engaged and floated thereby. Thereafter, the suspending equipment or crane may be removed and the cover will be maintained under proper pressure by the air compressor 19 and may be leveled or trimmed with internal ballast through the ballast header 31.

The installation may be further facilitated by providing a plurality of radially extending rods or cables 40,

preferably one for each cell 13, between flange 14g of hub 14 and flange 15b of ring 15, after the hub has been lowered into position but before unfurling the cells 13. The rods or cables 40 may be connected to flange 15 by turnbuckles 4th: for centering the hub and equalizing the tensions thereon. The cells may then be more easily unfurled and led out along the rods or cables 44) for attachment to the ring E5. in some instances the lower wall tile of each cell may be secured therealong to a cable 4% by providing a groove or channel 41 in which the cable is retained. After inflation of the cells 1.3, the rods or cables 49 may be either left in place or removed since the semi-rigid condition of the distended cells provide sufficient support for the rigid members 14 and 15.

It will be observed that the large dead air spaces between the upper and lower walls of cells 13 affords an insulating barrier which serves to prevent loss of heat from the digester thereby preserving the efiiciency of the digestion process. Of course, the gas collected in the chamber 16 and led olf via conduit 17a may be utilized for fuel in heating means for the tank.

Referring now to FIGS. 6 and 7, there is illustrated therein another embodiment of the invention wherein a cover 5% is disposed in tank 51, and comprises a plurality of inflatable cells 53 in a circular array about a center plate 54 and surrounded by a rigid peripheral ring 55. In this embodiment the air cells 53 comprise a lower wall 53a sloping inwardly and downwardly from the lower edge of ring 55 to center plate 54, a vertical wall 53b secured to ring 55', and a sloping upper wall 53c extending from the upper edge of ring 55 to join wall 53a at a place intermediate the ring 55 and center plate 54. The air cells formed thereby are inflated to provide the necessary buoyancy to the cover 50 and provide a saucer-shaped structure adapted to retain water therein for providing ballast. For this purpose, a submersible pump 57 is mounted on plate 54 and is provided with a flexible conduit 58 through which water may be pumped for increasing and decreasing the ballast load on the cover. A safety ovenflow drain pipe 59 is mounted on plate 54 and serves to drain oil to the tank 51 any ballast or rain water over a predetermined level to prevent sinking of the cover.

Ring 55 is channel-shaped in section and provides an annular, downwardly facing, chamber 60 for the collection of gases which rise in tank 51 and are led by the sloping cell wall 53:: to the edges of the cover. A flame arrestor and pressure relief valve assembly 61 is mounted atop ring 55 and is connected to a flexible conduit 61a for carrying off the collected gases.

A pipe 53, having an angled discharged nozzle 63a, depends from the upper wall of ring 55 into chamber 6t? and is connected to a flexible conduit 63/) for introducing or discharging raw sludge and supernatant into tank 51.

An air supply header 65' is mounted on the inner wall of ring 55 and is in communication with each of the cells 53 for suplying air under pressure thereto. Header 65 is connected to a suitable pump, not shown, or other source of air pressure and is provided with means for bleeding off abnormally high pressures such as may occure with increases in ambient temperatures.

The outer ring 55 comprises inwardly directed flanges 55a and 55b to which the cells 53 may be connected in a manner similar to that described with reference to the earlier described embodiments. Also, cables 67 may extend from center plate 54 to ring 55 to aid in the support of the air cells 53 and the center plate. Moreover, the ring 55 is provided with roller means 550 in engagement with tank 51, and comprises an extended outer wall, the lower edge 55d of which serves as a scum retaining baflle.

Another cover embodying the invention is illustrated in FIGS. 8 and 9 in which a cover 7b in a tank 71 comprises a single circular air cell 73 surrounded by a rigid ring 75.

In this instance the air cell 73 comprises a single cornpartment but may be divided into a number of compartments to insure against complete loss of buoyancy in the event of a rupture of the cell wall. Ring 75 is rectangular in section and defines an annular void 76 therein in which an air compressor 77 may be mounted for supplying air pressure to cell 73 through inlet conduit 77a under the control of valve 77b. Likewise, a ballast pump, not shown, may be located in void 76 for introducing and removing ballast water from the cell 73. As in the other embodiments, the outer ring 75 may include roller means 75a as required for reducing friction upon vertical movement of the cover 7t? as the liquid level in the tank rises and falls.

The outer edge of cell 73 is received between upper and lower flanges 75b and 75c of ring 75, and may be secured thereto by cementing or by means of flaps and studs as shown in the embodiment of FIG. 4. Also, cables 80 may be attached to lower flange 750 to span ring 75 for support of air cell 73. Instead of cables, suitable mesh netting may be used in this and in the other forms described.

An inspection port or manway 81 is provided in the upper wall 75d of ring 75 and is normally closed by a suitable hatch or plate 81a.

An additional modification is illustrated in FIG. 10 wherein there is shown a cover 99, similar to earlier described cover 12, and including a plurality of cells 91 connected to a central hub 92 and surrounded by a ring 93. in this modification, however, central hub 92 is closed at the bottom 92:: and does not function as a gas collector. An inspection or access cover 92]; is provided at the top of hub 92, as well as an air compressor 95 which functions in the same manner as compressor 19 of cover 12.

From the foregoing detailed descriptions and accompartying drawings of several preferred forms of floating covers embodying the present invention, it will be appreciat d that there has been provided thereby an improved cover structure which leads to economy in manufacture, as well as in assembly and use. it will also be appreciated that the inflatable and collapsible cells, used in conjunction with a rigid, but light outer ring member, has provided a floating cover structure which combines the advantages of economy in manufacture, ease in assembly and adaptability to permit cleaning of the tank, without sacrificing other desirable functions such as insulating, gas collection, scum control and the like, necessary to the proper operation of a digester tank.

Although the present invention has been described with detailed reference to specific cover structures embodying the invention, and with reference to their use in digestion tanks, it will be understood that the invention is not limited to those specific structures, but rather, the invention includes all such changes, adaptations and uses as are reasonably embraced by the scope of the claims hereof.

Having described our invention, we claim:

1. in a tank structure having vertical wall portions, a cover adapted to float on the matter in said tank and con strained by said wall portions for vertical movement in said tank; said cover comprising a plurality of inflatable cells formed of normall limp sheet material which is gas impervious and compatible with said matter in the tank, said cells when inflated being adapted to rest on a major portion of the surface area of liquid matter in said tank, and a rigid peripheral member disposed in a substantially horizontal plane and in guided relation with said wall portions for vertical movement in said tank; said cells being inflated by gas under pressure so as to be distended thereby into engagement at their outer edge portions only with said rigid member; said rigid member serving to secure said cells together to form a unitary cover structure, said rigid member comprising a metal ring which is channel shaped in section to removably receive the outer edges of 7 said cells, said ring comprising means for guiding with respect to said Wall portions.

2. In a tank structure for holding liquid matter and having side walls; a cover constrained by said walls for vertical movement and adapted to float on the matter in said tank, said cover comprising a plurality of inflatable cells formed of normally limp sheet material which is gas impervious and compatible with said matter in the tank, said cells when inflated being adapted to rest on a major portion of the surface area of liquid matter in said tank, a rigid outer member disposed in a substantially horizontal plane and in guided relation with said wall for vertical movement in said tank, and a centrally disposed hollow rigid inner member, said outer member having an inwardly facing annular groove and said inner member having an outwardly facing annular groove; said cells being disposed in a circular array between said inner and outer members; said cells being distended by gas pressure therein into engagement with said annular grooves so as to form a unitary cover structure, one of said rigid members comprising a header communicating with the interior of each of said cells, and flexible conduit means leading from said header for conveying ballast liquid to and from said cells for varying the flotation characteristics thereof.

3. A floating cover structure for use in a cylindrical tank for containing liquid matter, said cover structure comprising a rigid outer ring member adapted to be disposed in guided but spaced relation to the wall of said tank for vertical movement therein, a hollow rigid inner member disposed centrally of said ring member, a plurality of individual wedge shaped inflatable cells disposed in a circular array between said ring and inner members so as to rest on a major portion of the surface area of thereof liquid matter contained in said tank, said cells being formed of normally limp sheet material which is impervious to inflating gas and compatible with said liquid matter, and a plurality of support elements extending radially from said inner member to said ring member and beneath said inflatable cells, said cells and support elements having their outer and inner ends respectively releasably secured to said ring and inner members so that one or more of said cells may be deflated and furled to provide access to the interior of said tank while the remaining cells provide flotation for said cover structure.

4. A floating cover structure as deiined in claim 3 and comprising first conduit means in communication with said individual cells for maintaining a predetermined gas pressure therein, and second conduit means in communication with said individual cells for admitting and removing ballast liquid to and from said individual cells, said second conduit means comprising valve means for selectively ballasting inflated cells on the side of said cover structure opposite deflated and furled cells so that said cover structure may be maintained in a horizontal plane. 5. A structure as defined in claim 1 and wherein said rigid member comprises a header, means for selectively placing said header in communication with the interiors of a plurality of said cells, and flexible conduit means leading from said header for conveying ballast liquid to and from the cells communicating with said header for varying the flotation characteristics of said structure.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A TANK STRUCTURE HAVING VERTICAL WALL PORTIONS, A COVER ADAPTED TO FLOAT ON THE MATTER IN SAID TANK AND CONSTRAINED BY SAID WALL PORTIONS FOR VERTICAL MOVEMENT IN SAID TANK; SAID COVER COMPRISING A PLURALITY OF INFLATABLE CELLS FORMED OF NORMALLY LIMP SHEET MATERIAL WHICH IS GAS IMPERVIOUS AND COMPATIBLE WITH SAID MATTER IN THE TANK, SAID CELLS WHEN INFLATED BEING ADAPTED TO REST ON A MAJOR PORTION OF THE SURFACE AREA OF LIQUID MATTER IN SAID TANK, AND A RIGID PERIPHERAL MEMBER DISPOSED IN A SUBSTANTIALLY HORIZONTAL PLANE AND IN GUIDED RELATION WITH SAID WALL PORTIONS FOR VERTICAL MOVEMENT IN SAID TANK; SAID CELLS BEING INFLATED BY GAS UNDER PRESSURE SO AS TO BE DISTENDED THEREBY INTO ENGAGEMENT AT THEIR OUTER EDGE PORTIONS ONLY WITH SAID RIGID MEMBER; SAID RIGID MEMBER SERVING TO SECURE SAID CELLS TOGETHER TO FORM A UNITARY COVER STRUCTURE, SAID RIGID MEMBER COMPRISING A METAL RING WHICH IS CHANNEL SHAPED IN SECTION TO REMOVABLY RECEIVE THE OUTER EDGES OF SAID CELLS, SAID RING COMPRISING MEANS FOR GUIDING THEREOF WITH RESPECT TO SAID WALL PORTIONS. 